Quasicontinuum study of the shear behavior of defective tilt grain boundaries in Cu

Abstract

Atomistic simulations using the quasicontinuum method are used to study the role of vacancy defects and angström-scale voids on the mechanical behavior of five tilt bicrystals containing grain boundaries (GBs) that have been predicted to exhibit characteristic deformation processes of nanocrystalline and nanotwinned metals : GB-mediated dislocation emission, interface sliding, and shear-coupled GB migration. We demonstrate that such nanoscale defects have a profound impact on interfacial shear strength and underlying deformation mechanisms in copper GBs due to void-induced local stresses. In asymmetric high and low angle GBs, we find that voids become preferential sites for dislocation nucleation when the void size exceeds 4 Å. In symmetric Σ9(221) GBs prone to sliding, voids are shown to shield the local shear stress, which considerably reduces the extent of atom shuffling at the interface. In symmetric Σ5(210) and Σ27(115) GBs, we find that the effect of voids on shear-coupled GB migration depends on the GB tilt direction considered, as well as on the size and number of voids. Remarkably, large voids can completely abate the GB migration process in Σ27(115) GBs. For all GB types, the interfacial shear strength is shown to decrease linearly as the volume fraction of voids at the interface increases ; however, this study also suggests that this decrease is much more pronounced in GBs deforming by sliding than by dislocation nucleation or migration, owing to larger void-induced stresses.

Symmetric and asymmetric tilt grain boundary structure and energy in Cu and Al (and transferability to other fcc metals)

“…Many of the early studies (e.g., [5,6]) focused on understanding the grain boundary structure and energy. However, recent studies have expanded to address grain boundary sliding [7][8][9][10], migration and bulk dislocation slip transfer [11][12][13], grain boundary fracture [14][15][16] or spall [17][18][19][20], grain boundary segregation [21][22][23], phase transformations [24], grain boundary mobility [25,26], etc. In many cases, grain boundary structures have to be recreated in order to assess properties, and it is unclear whether the minimum energy structure was used or a higher energy metastable structure; hence, openly publishing grain boundary datasets in materials repositories can aid in providing a common starting configuration for these studies.…”

Quasicontinuum Simulation of the Effect of Lotus-Type Nanocavity on the Onset Plasticity of Single Crystal Al during Nanoindentation

“…The results showed that the onset plasticity was substantially diminished by the corresponding dislocation nucleation from the inner side of the cavities. Using the QC model, Péron-Lührs et al [ 37 ] investigated the effect of nanosized cavities at grain boundaries on the shear behavior of grain boundaries in Cu. Their results showed that the nanocavities could impede atom shuffling across the interfaces, preferentially facilitate the initiation of dislocation at cavities, and soften grain boundaries, resulting in a decrease of the yield strength.…”